Acid zinc electrodepositing



United States Patent US. Cl. 204-55 Claims ABSTRACT OF THE DISCLOSURE Acid zinc electrodepositing baths containing a minor amount, effective to impart brightness to electrodeposited zinc, of a bath-compatible hydrolyzed protein, a minor amount, effective to inhibit formation of rough edges on a metallic article whereon zinc is being electrodeposited due to the depositing zinc, of ions of a metal of Group VI-B of the Periodic Table, and preferably, as a ductilizer and booster-brightener for the zinc, a bath-compatible sulfur-containing compound of the formula: HSCH COOR wherein R is hydrogen or a bath-compatible hydrophilic cation. The zinc electrodeposits obtained from electrodepositing baths of this invention exhibit a considerably improved resistance to corrosion by salt spray.

This invention relates to the electrodeposition of zinc and more especially to new and improved acid zinc electrodepositing baths from which zinc of superior physical properties and considerably improved salt spray corrosion resistance can be deposited, and new additive compositions for use in providing the improved acid zinc baths. The invention also relates to an improvement in the method for electrodepositing zinc.

Hydrolyzed protein of animal origin, such as peptones obtained by the enzymatic digestion or degradation of, for instance, gelatin obtained from horses boots, and animal stomach linings, are known in the prior art as brightener additives for acid zinc electroplating baths. We tried hydrolyzed protein of animal origin as a brightener for acid zinc electroplating baths and, while we also found the hydrolyzed protein to result in brighter zinc deposits, the ferrous metal strips being plated were found to undesirably have rough and uneven surfaces at the edges of the strips due to a non-uniform plating and iling up of the zinc. Further, the zinc electrodeposits were quite brittle and of low ductility and there was also room for improvement from the standpoint of the brightness of the zinc deposit.

One object of this invention is to provide new and improved acid zinc electrodepositing baths.

Another object of this invention is to provide new and improved acid zinc baths for producing zinc electrodeposits of considerably improved brightness.

Another object of this invention is to provide new and improved acid zinc baths enabling the production of bright lustrous zinc electrodeposits, while avoiding the formation of rough edges on the article or articles, for instance ferrous metal strips, sheet or continuous ribbon, on which the zinc is being electrodeposited due to the depositing zinc.

Another object is to provide new and improved acid zinc electroplating baths capable of producing zinc electrodeposits of considerably improved resistance to corrosion by salt spray.

A further object is to provide new and improved acid zinc electroplating baths capable of producing zinc electrodeposits of good ductility.

A further object is to provide new additive compositions especially well suited for addition to acid zinc electrodepositing baths.

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A further object is to provide new additive compositions for zinc electroplating baths which enable the production of bright zinc electrodeposits 0f considerably improved salt spray corrosion resistance, while inhibiting or eliminating the formation of rough edges on the article or articles on which the zinc is being electrodeposited due to the depositing zinc.

Another object is to provide an improvement in the method for the electrodeposition of zinc.

Additional objects and advantages will be apparent as the invention is hereinafter described in detail.

In accordance with the present invention, We have found that by the utilization in the rior acid zinc elec trodepositing baths of the combination of ions of a metal of Group VI-B of the Periodic Table and a bath-compatible hydrolyzed protein, acid zinc electrodepositing baths are attained which produce not only bright zinc deposits but also zinc deposits of considerably improved resistance to corrosion by salt spray. In addition, the present invention avoids or eliminates the development or formation of any or substantially any rough edges on the article or articles on which the zinc is being electrodeposited due to the depositing zinc. Such article or articles, usually flat-surfaced metallic articles, for instance ferrous metal strips or sheets or continuous ribbons, have been subjected to an edge-cutting operation heretofore after the zinc plating to trim off the rough, uneven edges due to the uneven deposition of the zinc, and such edge cutting or trimming operation with the attendant expensive cutting apparatus is no longer required by virtue of this invention.

In addition to electroplating baths, the addition agents herein can be incorporated in or added to acid zinccontaining baths or solutions from which Zinc is to be recovered by electrowinning. Accordingly, the term acid zinc electrodepositing bath or baths is used herein in the broad sense to include not only acid zinc baths for electroplating articles immersed therein but also acid zinc-containing baths or solutions for the electrowinning recovery of zinc.

The acid zinc bath can also contain, in accordance with a preferred embodiment of the invention, as a booster brightener and a ductilizer, i.e. an agent or material rendering the zinc electrodeposit appreciably less brittle and appreciably more ductible, a bath-compatible sulfur-containing compound capable of providing sulfhydryl groups in the bath and of acting or functioning therein as a booster brightener and ductilizer for the zinc. Exemplary of such sulfur-containing compounds are organic compounds represented by the formula HSCH COOR wherein R is a hydrogen atom or a bath-compatible, hydrophilic, i.e. water-loving, salt-forming inorganic cation, for instance an alkali metal cation, e.g. a Na or K cation, or a non-metal cation, for instance an NH cation. In its capacity as a booster-brightener, such compatible sulfur-containing compound acts synergistically with the hydrolyzed protein to produce a materially brighter zinc deposit than does the hydrolyzed protein alone as brighteners. Also exemplary of such sulfur-containing compounds is an inorganic compound such as sodium tetrasulfide, i.e. Na S which reacts in the bath to pro- -vide free sulfhydryl groups therein. The preferred compound capable of providing the sulfhydryl groups in the bath is thioglycolic acid. The hydrophilic cation can be substituted therein for the carboxy hydrogen, when desired, by admixing the thioglycolic acid with an aqueous solution of NaOH, KOH or NH OH at room temperature. The thioglycolic acid and Na S are obtainable in commerce. By the term bath-compatible used herein is meant a material or compound that will accomplish its intended function in the acid zinc electrodeposition bath and is harmless therein and will not adversely affect the deposition of zinc from the bath or introduce materials or ions therein adversely affecting the bath or the zinc deposition from the bath.

The mechanism or theory behind the considerably improved corrosion resistance provided by this invention is not presently known, and such improve-ment was unexpected and surprising. Also unexpected was the synergistic enhancement of the brightness of the zinc deposit provided 'by the sulfhydryl group-providing Compound in the bath together with the hydrolyzed protein, the elimination of the rough edges on the article having zinc deposited thereon, and the ductility of the zinc deposit provided by the sulfhydryl group-providing compound.

Although it is preferred to incorporate into or add to the acid zinc electrodepositing bath prior to electrodepositing the hydrolyzed protein and the Group VI-B metal ions together in an additive composition, such materials can be added separately to the acid zinc bath. The sulfhydryl group-providing compound is preferaby added separately to the acid zinc bath prior to the electrodepositing.

The metal ions utilizable herein are chromium, tungsten and molybdenum ions. With the chromium ions the trivalent state is essential, with hexavalent chromium ions being unsatisfactory due to blistering of the metallic electrodeposit resulting with use of the hexavalent chromium. Further, the hexavalent chromium ions result in an undesirable oxidation of a portion of the organic constituents of the bath.

The Group VI-B metal ions are provided in the acid zinc plating bath by being incorporated into or added to the bath as a bath-compatible compound which is water soluble or bath soluble. Thus the trivalent chromium ions are provided in the bath by addition as a wateror bath-soluble trivalent chromium salt, e.g. as a soluble chromic sufate or chromium ammonium sulfate. The molybdenum and tungsten ions are provided in the bath by addition as a water-soluble or bath-soluble compound, for instance as ammonium heptamolybdate, molybdenum tetrachloride, molybdenum trioxide and phosphotungstic acid. The Periodic Table herein is the Periodic Chart of The Elements, Handbook of Chemistry and Physics, 39th edition, published by Chemical Rubber Publishing Company, pages 400-401.

The Group VI-B metal ion is added to the acid zinc electrodepositing bath as a soluble compound of the Group VI-B metal ionizable to yield the Group VI-B metal ions, in a minor amount effective to inhibit or eliminate the formation of rough edges on the article or object being electrodeposited with zinc due to the depositing zinc, preferably within the range of about 0.02-0.24 gram per liter of bath; the hydrolyzed protein is added to the acid zinc bath in a minor amount, effective to impart brightness to the electrodeposited zinc, as an enzymatically degraded meat protein of animal origin in an effective amount preferably within the range of about 0.1-1 gram per liter of bath; and the sulfhydryl group-providing compound, when utilized, is added to the acid zinc electropositing bath in a minor amount sufficient to act as a zinc ductilizer and booster brightener for the zinc, preferably within the range of about 0.01-0.15 gram per liter of bath. As a booster brightener for the zinc, the sulfhydryl groupproviding compound acts synergistically with the hydrolyzed protein to produce an appreciably or materially brighter zinc deposit than does the hydrolyzed protein alone. Other protein hydrolysates utilizable herein are essentially each added to the acid zinc bath in an effective amount within the range of 0.1-0.8 gram per liter of bath. Such other protein hydrolysates, which are of animal, yeast and vegetable origin and are hereinafter disclosed are utilized in the acid zinc bath in the effective amounts hereinafter specified, all of which are within the 0.1-0.8 gram per liter range.

A typical commercial acid zinc plating bath improved upon by the present invention contains water as solvent or gallon, and an inorganic acid such as, for instance, boric acid (H in amount from about 2-4 ounces per gallon. The hydrogen ion concentration (pH) of such a bath is about 2. Other acid zinc plating baths having a pH of about 3 can also be improved upon in accordance With the invention. A conductive salt, for instance ammonium fluoride (NH F) or ammonium chloride (NH Cl) can be added to the bath, if desired, in amounts of about 2-4 ounces per gallon. Such baths are useful for electrodepositing zinc electrodepositing conditions including a temperature range ranging from about 80 F.- F. and conventional current densities well known in this art.

In another embodiment of the invention, a liquid additive composition is provided which is especially well suited for addition to the acid znc electroplatng bath to achieve electrodeposition of zinc of the superior physical properties and considerably improved salt spray corrosion resistance discussed elsewhere herein. Such additive composition comprises an aqueous solution of the bath-compatible hydrolyzed protein and the Group VI-B metal ions. The amounts of hydrolyzed protein and Group VI-B metal ion that can be present in this liquid additive composition are not especially critical and can be carried over quite Wide ranges. The hydrolyzed protein is typically present in such additive composition in amount of a out 2%4% by weight, and the Group VI-B metal ions, preferably the trivalent chromium ions, as the soluble compound of the Group VI-B metal typically in amount of 1%-8% by weight (percentages based on total additive composition). The liquid additive composition preferably also contains a moldand bacteria-growth inhibitor, for instance a sodium salt of 2,4,5-trichlorophenol marketed under the trademark name Dowacide B, and a perfume or perfuming agent for instance that marketed under the trade name Compound 40-R-10501. The two last-mentioned materials when employed in the additive composition are present therein in a minor amount, sufficient to inhibit the growth of mold and bacteria and to perfume or mask the order of the composition and mold-growth inhibitor. Typical amounts of the moldand bacteriagrowth inhibitor and the perfuming agent utilized are specified in Example III herein. Such liquid additive composition is added to the conventional aqueous acid zinc plating bath in minor amount suflicient to impart brightness, salt spray corrosion resistance and smooth edges to the electrodeposited zinc. The exact amount of the liquid additive composition added to the acid zinc bath will be dependent on the particular proportions or amounts of hydrolyzed protein and Group VI-B metal ion in solution therein, and preferably will be that amount providing an amount of hydrolyzed protein and Group VI-B metal ion in the bath within the preferred ranges of these materials previously specified herein.

In another embodiment, a solid additive composition is provided for the acid zinc electroplating bath and such solid additive comprises a mixture of the acid zinc bathcompatible hydrolyzed protein, and the bath-compatible water-soluble compound of the Group VI-B metal preferably in fine size particulate form. Such Group VI-B metal compound is ionized in water or the aqueous solution to yield or provide Group VI-B metal ions. The amounts or proportions of hydrolyzed protein and soluble Group VI- B metal compound in such solid additive are not especially critical and can be varied over fairly wide ranges. The hydrolyzed protein is typically present in such solid additive in amount of about 40%-50% by weight and the soluble ionizable Group VI-B metal compound typically in amount of about 60%-50% by weight (percentages based on total additive composition). This solid additive composition can also contain a filler material, if desired for instance a water-soluble zinc salt such as zinc sulfate (ZnSO which serves the dual function of supplying zinc sulfate to the electro-depositing bath for the electrodepositing as well as being a filler.

The preferred hydrolyzed protein herein is one which has first been subjected to a preliminary treatment involving acidifying an aqueous solution of the hydrolyzed protein to about pH 2-3.5 whereby a flocculant precipitate forms, followed by separating the precipitate by filtration or otherwise from the aqueous solution of hydrolyzed protein. The filtered oif precipitate is discarded. The remaining solution of hydrolyzed protein can be utilized as such for preparing the liquid additive composition herein, or in the case of the solid additive composition herein, the water is evaporated olf to leave the solid protein hydrolysate which is mixed together with the soluble ionizable Group VI-B compound in forming the solid additive.

More specifically, the preliminary treatment of the hydrolyzed protein prior to its addition to the acid zinc bath or its use in preparing the additive composition, involves dissolving the hydrolyzed protein in fine particulate form, for instance an enzymatically degraded or digested meat protein in finely divided form, in water at an elevated temperature of about 120 F. up to but below the boiling point of water at atmospheric pressure, followed by lowering the pH of the solution by acidification to about pH 2-3.5 whereby a flocculant precipitate forms. The fluocculant precipitate is then separated from the aqueous solution of the protein by, for instance, filtration and the filtered ofi precipitate discarded. The acidification of the aqueous protein solution to lower its pH to about 2-3.5 can be effected by the addition of sulfuric acid, although other inorganic or organic acids could be utilized instead. However, when a lead container is used for holding the bath, which is typically the case, neither a halogen acid nor acetic acid should be used for the acidification for the reason the lead of the container would be attacked by such acids. However, when the container is one fabricated of a material other than lead and which is chemically inert to the halogen acid or acetic acid, such acid can be utilized for the acidification.

The hydrolyzed protein herein is usually a protein hydrolysate of animal origin, although a protein hydrolysate of plant or vegetable origin can be utilized with good results. Enzymatically-degraded meat proteins, certain of which are used as bacteriological nutrients, are obtainable in the commercial market. Exemplary of such enzymatically-degraded meat proteins herein are the protein hydrolysates obtained by subjecting the meat to the action of a pancreatic or similar proteolytic enzyme. As available and shipped in commerce, the enzymaticallydegraded or digested meat is in the form of a dry powder containing up to about 5% of water. About 95% of the commercial product consists largely, if not entirely, of hydrolyzed meat protein, fatty acids and hydrocarbons. The fatty acids and hydrocarbons can total as much as of the commercial product. The remainder, approximately 65% of the commercial product, is proteinaceous material that is virtually completely hydrolyzed. The commercial product contains about 14% total nitrogen. A typical commercial enzymatically-degraded or digested meat protein utilized in this invention shows the following analysis:

5 Nitrogen: Percent by wt. Phenylalanine 1.8 Threonine 1.6 Leucine 3.5 Isoleucine 2.5 Valine 2.9 Glutamic acid 9.1 Glycine 5.1 Aspartic acid 5.9 Proline 4.8 Alanine 4.0

Exemplary of other protein hydrolysates utilizable herein are the enzymatic degradation products of casein, the enzymatic degradation products of soybean, and the enzymatic degradation products of yeast. Additional examples of protein hydrolysates utilizable herein with the quantities essentially to be used for each hydrolysate, given in grams per liter of bath, are those of animal origin marketed as Cosmetic Polypeptide #377, 0.1- 0.4; Cosmetic Polypeptide #B-315, 0.1-0.4; Edamin 50J8, 0.2-0.5; Solubilized Gelatin, 0.3-0.6; Protein Hydrolysate F-400, 0.2-0.5; Proto Peptone #159, 0.2- 0.5; Proto Peptone #627, 0.2-0.5; Proto Peptone #851, 0.2-0.5; Polypeptide AAS," 0.1-0.4; Polypep tide #37, 0.1-0.4; Polypeptide LSN, 0.1-0.4; Sole- Onic HAP, 0.2-0.5; Sol-U-Pro, 0.4-0.7; Granular Gelatin 2XPF, 0.5-0.8; and Hydrolyzed, Soluble, Animal Protein, 0.1-0.4; that of vegetable origin marketed as Soy Peptone, 0.2-0.5; and those of yeast origin marketed as Yeast Hydrolysate Type A, 0.2-0.5; Yeast Hydrolysate Type M, 0.2-0.5; Dry Yeast Autolysate Type 99F, 0.3-0.6; and Saroma, 0.2-0.5. All of the foregoing protein hydrolysates are readily obtainable in commerce. The protein hydrolysate utilizable herein can also be the non-enzymatic degradation product of lambs wool. The last-mentioned product is obtained by degrading lambs wool by contacting same with concentrated KOH until degradation of the wool has occurred, followed by acidification with sulfuric acid to a pH of about 2-3.5, filtering off the precipitate formed as a result of such acidification, and diluting the remaining solution with water.

The hydrolyzed meat protein of animal origin preferred for use herein is that obtained by dissolving an enzymatically-degraded meat protein in water at a temperature of about F. up to but below the boiling point of water, followed by lowering the pH of the solution by acidification to about pH 2-3.5 whereby a flocculant precipitate forms. The flocculant precipitate is separated, for instance by filtration, from the aqueous solution of hydrolyzed meat protein, and the filtered off precipitate discarded.

The following examples of additive agent compositions of this invention are illustrative only and in no way restrictive. The chromic sulfate was the water-soluble Cr (SO -5H O obtained in commerce under the trade name Tanolin.

EXAMPLE I Percent by wt. Meat protein hydrolysate 3 Chromic sulfate 4 Water 93 EXAMPLE II Percent by wt. Meat protein hydrolysate 3 Chromic sulfate 2.7 Water 94.3

EXAMPLE III Percent by wt. Meat protein hydrolysate 3 Chromic sulfate 4 Water 92.94 Dowacide B 0.02 Perfume 40-R-10501 0.04

7 EXAMPLE IV Percent by wt. Vegetable protein hydrolysate 3 Ammonium heptamolybdate 2 Water 95 EXAMPLE V Percent by wt. Vegetable protein hydrolysate 3 Phosphotungstic acid 1.3 Water 95.7

EXAMPLE VI Percent by wt. Meat protein hydrolysate 3 Chromic sulfate 8 Water 88.94 Dowacide B 0.02 Perfume 40-R-10501 0.04

The following Example VII is illustrative of the method of formulating the additive agent composition herein but in no way restrictive.

EXAMPLE VII Fifty (50) lbs. of a meat protein hydrolysate powder of commerce, which was an enzymatically degraded meat protein, were dissolved in 80 gallons of hot water of temperature of 160 F. in a stainless steel tank. Sulfuric acid was admixed with the resulting solution in amount sufiicient to lower its pH to 3.5, after which the acidified solution was mixed for two hours. A flocculant precipitate formed as a result of the acid addition and mixing, and was filtered from the solution and discarded. Eleven (11) fluid ounces (330 0.0.) of Perfume 40R-10501 was then added to the resulting solution of protein hydrolysate, as a perfuming agent to mask the odor of the meat protein hydrolysate. Four (4) ounces of Dowacide B was also added to the solution of protein hydrolysate to inhibit the growth of mold and bacteria therein. The Dowacide B and Perfume 40-R-l 0501 are obtainable in commerce.

Sixty-seven (67) lbs. of chromic sulfate, i.e.

Cr (804)13 SH O were admixed with 100 gallons of hot Water of temperature of 185 F. Sulfuric acid was added to the resulting solution in amount sufficient to reduce its pH to 3 thereby to maintain the trivalent chromium in solution. Two (2) ounces of Dowacide B were also added to the solution of chromic sulfate as a mold and bacteria inhibitor.

The filtered aqueous solution of meat protein hydrolysate referred to supra, and the aqueous solution of chromic sulfate were then mixed together to form the product addition agent composition, and the resulting mixture poured into bottle containers for marketing.

The test data of Examples VIII and IX which follow show the considerable improvement in brightness and corrosion resistance respectively of the zinc electrodeposits obtained with the aqueous acid zinc bath of this invention.

EXAMPLE VIII Three mild steel cylinders each of diameter and 3" length were each separately rotated in an aqueous acid zinc electroplating bath at a rotation rate equivalent to a surface speed of the cylinder of about 100 feet per minute. One of the cylinders, designated Cylinder A, was electroplated with zinc at an average current density of about 200' amperes per square foot in the commercial aqueous acid zinc plating bath the composition of which is previously disclosed herein, at a bath temperature of about 125 F. and to which had been added trivalent chromium ions as a soluble chromic salt, hydrolyzed meat protein and thioglycolic acid in amounts of about 0.08 gram per liter, 0.3 gram per liter and 0.07 gram per liter, respectively.

Another of the mild steel cylinders, designated Cylinder B, was plated with an additives-containing zinc plating bath of substantially the same composition and by similar procedure as used in plating Cylinder A except that the average current density employed for zinc plating Cylinder B was 400 amperes per square foot.

The remaining mild steel cylinder, designated Cylinder C, was plated with the commercial aqueous acid zinc plating bath the composition of which is previously disclosed herein except that none of the additives of this invention were added to the bath, i.e. no trivalent chromium or other Group VI-B metal ions, no hydrolyzed protein and no thioglycolic acid or other sulfhydryl groupproviding compounds, were added to the bath. Cylinder C was plated employing the current density and bath temperature utilized for plating Cylinder A. The results of such plating test runs are set forth hereafter in Table A:

TABLE A Brightness of Grain structure zinc Deposit of zinc deposit Ductility Cylinder:

r Excellent Fine Good.

do do Do. C Poor Coarse Non-ductile and brittle.

EXAMPLE IX Four mild steel cylinders each of diameter and 3" length were rotated two cylinders per bath in four separate aqueous acid zinc plating baths at a rotation rate such as to provide a cylinder surface speed of about I20 feet per minute. The current density averaged 150 amperes per square foot in each bath and the temperature of each bath was about F. Two of the cylinders, designated Cylinders D and E, were plated in a conventional aqueous acid zinc plating bath of the composition previously disclosed herein and to which no additives of this invention were added; and two of the cylinders, designated Cylinders F. and G, were plated in the commercial acid zinc plating bath of composition previously set forth herein to which had been added trivalent chromium ions, hydrolyzed meat protein and thioglycolic acid in amounts of about 0.08 gram per liter, 0.3 gram per liter, and 0.07 gram per liter, respectively.

Cylinders D and E, and F and G were taken directly from their respective plating baths and subjected to a salt-spray corrosion test of ASTM designation B 117- 62T. The results of the corrosion tests are set forth in Table B which follows:

White corrosion The considerable improvement in salt spray corrosion resistance provided by this invention is shown by the data of Table B, In the test results of Table B, the time elapsing until Red Rust is the important test result. Thus Cylinders F and G, plated from the acid zinc bath containing the additives of this invention, exhibited no red rust until 192 hours. This was 48 hours longer and a 33 /3% improvement over Cylinders D and E, plated from the commercial acid zinc bath containing no additives of this invention, which showed red rust at 144 hours.

The new and improved electrodepositing baths of this invention are eminently well suited for the zinc plating of ferrous and non-ferrous strip, sheet and continuous ribbon, for instance steel and copper strip, sheet and continuous ribbon. In addition to being bright and lustrous, free of rough edges on the article plated, and substantially non-brittle and ductile, the zinc electrodeposits herein are of fine grain microstructure and are continuous depostis free or substantially free of discontinuities in the zinc deposit.

It is also within the spirit and csope of this invention that, in subcombination, the Group VI-B metal ions or the sulfur-containing compound capable of providing the sulfhydryl groups and of acting as a ductilizer for the zinc be incorporated or added singly to the acid zinc electrodepositing bath. By the addition of but one of these additives, the benefit of the particular additive can be realized in the electrodeposited zinc.

What is claimed is:

1. In a method for the electroplating of zinc, the improvement which comprises effecting the electroplating of the zinc from an aqueous acid zinc electroplating bath containing a source of zinc ions, a minor amount, effective to impart brightness to electrodeposited zinc, of a bath-compatible enzyme-degraded hydrolyzed protein, a minor amount, effective to inhibit formation of substantially any rough edges on a metallic article whereon zinc is being electrodeposited due to the depositing zinc, of ions of a metal of Group VI-B of the Periodic Table, and a minor amount, sufiicient to yield a ductile and appreciably brighter zinc electrodeposit, of a bath-compatible sulfur-containing compound of the formula: HSCH COOR wherein R is from the group consisting of a hydrogen atom and a bath-compatible hydrophilic cation, the zinc electroplate exhibiting a considerably improved resistance to corrosion by salt spray.

2. In a method for the electroplating of zinc wherein the zinc is electroplated from an aqueous acid zinc electroplating bath containing a source of zinc ions, the improvement which comprises, prior to effecting the electroplating of the zinc from the acid zinc bath, incorporating into the bath a minor amount, effective to impart brightness to electrodeposited zinc, of a bath compatible enzyme-degraded hydrolyzed protein, a minor amount, effective to inhibit formation of substantially any rough edges on a metallic article whereon zinc is being electrodeposited due to the depositing zinc, of ions of a metal of Group VI-B of the Periodic Table, and a minor amount, sufiicient to yield a ductile and appreciably fbrighter zinc electrodeposit, of a bath-compatible sulfur compound of the formula HSCH COOR wherein R is from the group consisting of a hydrogen atom and a bathcompatible hydrophilic cation, the zinc electroplate exhibiting a considerably improved resistance to corrosion by salt spray.

3. An aqueous acid zinc electroplating bath containing a source of zinc ions, a minor amount, effective to impart brightness to electrodeposited zinc, of a bath-compatible hydrolyzed protein, a minor amount, effective to inhibit formation of substantially any rough edges on a metallic article whereon zinc is being electrodeposited due to the depositing zinc, of ions of a metal of Group VI-B of the Periodic Table, and in minor amount, sufficient to yield a ductile and appreciably brighter zinc electrodeposit, of a bath-compatible sulfur-containing compound of the formula: HSCH COOR wherein R is from the group consisting of a hydrogen atom and a bath compatible hydrophilic cation, the zinc electroplate obtained from said electroplating bath exhibiting a considerably improved resistance to corrosion by salt spray.

4. An aqueous acid zinc electroplating bath containing a source of zinc ions, a minor amount, effective to impart brightness to electrodeposited zinc, of a bath-compatible enzyme-degraded hydrolyzed protein, a minor amount, effective to inhibit formation of substantially any rough edges on a metallic article whereon zinc is being electrodeposited due to the depositing zinc, of ions of a metal of Group VI-B of the Periodic Table, and a minor amount, suflicient to yield a ductile and appreciably brighter zinc electrodeposit, of a bath-compatible sulfurcontaining compound of the formula: HSCH COOR wherein R is from the group consisting of a hydrogen atom and a bath compatible hydrophilic cation, the zinc electroplate obtained from said electroplating bath exhibiting a considerably improved resistance to corrosion by salt spray.

5. The electroplating bath of claim 4 wherein the enzyme-degrated hydrolyzed protein is an enzyme-degraded hydrolyzed meat protein.

6. The electroplating bath of claim 4 wherein the metal ions are trivalent chromium ions.

7. The electroplating bath of claim 4 wherein the organic sulfur-containing compound is thioglycolic acid.

8. The electroplating bath of claim 4 wherein the enzyme-degraded hydrolyzed protein is an enzymatically degraded hydrolyzed meat protein and is added to the bath in an effective amount within the range of about 0.1-1.0 gram per liter, the Group VIB metal ions in the form of a soluble compound of the Group VI-B metal in amount of about 0.020.24 gram per liter, and the sulfur-containing compound in amount of about 0.01- 0.15 gram per liter.

9. The electroplating bath of claim 4 wherein the enzyme-degraded hydroylzed protein is from the group consisting of enzyme-degraded protein hydrolysates of animal, yeast and vegetable origin and is added to the bath in an effective amount within the range of 0.1-0.8 gram per liter, the Group VIB metal ions as a soluble compound of the Group VI-B metal in amount of about 0.020.24 gram per liter, and the sulfur-containing compound in amount of about 0.0l0.15 gram per liter.

10. The electroplating bath of claim 4. wherein the enzyme-degraded hydrolyzed protein is an enzyme-degraded hydrolyzed meat protein and is subjected to a preliminary treatment, prior to its addition to the bath, involving dissolving the enzyme-degraded hydrolyzed meat protein in water at a temperature of about F. up to but below the boiling point of water, lowering the pH of the solution to about 23.5 whereby a flocculant precipitate forms, and separating the flocculant precipitate from the aqueous solution of the enzyme-degraded hydrolyzed meat protein.

References Cited UNITED STATES PATENTS 2,097,630 11/1937 Lutz 204-50 2,171,842 9/1939 Barrett et al 204-55 2,196,588 4/1940 Hull 204-55 2,451,426 10/ 1948 Bair et al 204-55 2,679,475 5/ 1954 Singler 204-43 2,700,646 1/1955 Chester 204-44 2,799,635 7/1957 Chester et al. 204-55 2,886,500 5/1959 Bride et al. 204-44 2,900,313 8/ 1959 Saubestre et al. 204-55 3,276,977 10/1966 Willmund et al. 204-55 XR 3,285,804 11/1966 Lindemann 20455 OTHER REFERENCES Chemical Abstracts, vol. 55, 24331f, (1961).

JOHN H. MACK, Primary Examiner G. L. KAPLAN, Assistant Examiner UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Dated April 7, 1970 Patent NO. 3 qon; Inventor(s) Gilbert J. Schaedler and John B. Winters It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 4, line 15 --under-- should be inserted after "zinc" and before "electrodepositing"; line 20, znc electroplat ng" should read --zinc electroplating--; line 44, "order" should read --odor--; line 65, "ionized" should read --ionizable--. Column 6, line 1, "Nitrogen" should read --Amino Acids (Cont'd) Column 9, line 12, "depostis" should read "deposits"; line 14, "csope" should read --scope--; line 66, "in" should read --a--. Column 10, line 18, "-degrated" should read -degraded SIGNED AND sun-:0 AUG 2 51970 NIH-IA! Ill. mm, B. Mnioner of Patents FORM PO-IOSO (10-69) USCOMM Dc 0876 F69 s 11.1. Govnmncm "nu-mo OFFICII nu o-su-un 

